In intrusion alarm systems, it is frequently necessary to employ more than one sensor in a system for protection of multiple areas or a large single area. As the number of areas protected by respective sensors increases, it becomes more important for a person responding to an alarm to be able to quickly and unambiguously determine which sensor or sensors have detected the intrusion which produced the alarm condition. Such an indication will allow a person responding to an alarm to go immediately to the particular area where an intrusion has been sensed. Furthermore, such a system will facilitate the determination and correction of transitory conditions producing false alarms. These false alarm conditions may no longer be present by the time a person has responded to the alarm condition, and having a definite indication of which sensor caused the false alarm is a helpful aid in determining what caused the false alarm. Additionally, testing of intrusion alarm systems having many sensors becomes more tedious as the number of sensors increase, frequently requiring evacuation of the protected areas in order to individually test each sensor and the associated alarm circuitry.